Over 90% of breast cancer (BCa) related deaths are a consequence of inoperable metastatic disease. Our preliminary findings suggest that FRY may be one of the critical molecules in controlling the fundamental histopathological changes of epithelial-mesenchymal transition (EMT), and regulating tumor progression and invasion/metastasis. Our proposed study is based on the following preliminary observations: 1) We identify Fry as a candidate Mammary Carcinoma Susceptibility gene by genetic linkage analysis in inbred rat of heritable mammary tumor; 2) Ectopic expression of wildtype rat Fry reverses the mesenchymal-like morphology of highly metastatic MDA-MB-231 BCa cells to epithelial cell differentiation and polarity; 3) Overexpression of wildtype rat Fry significantly reduce tumor growth and invasiveness in vitro and in vivo; and 4) Pathway network analysis of gene expression profiles in mammary epithelial (FRY-knockdown) and tumor cells (rat Fry-Knockin) indicates that FRY contributes to the maintenance of epithelial cell architecture, differentiation, motility, cell-to-cell signaling and cell adhesion; 5) Analysis of FRY in human clinical samples of BCa shows that decreased FRY protein levels are highly correlated with undifferentiated tumor histopathological features and increased tumor grade; and 6) Studies have suggested that FRY's functions appear directly association with its interaction with Hippo-NDR pathway. Based on these preliminary observations, we hypothesize that FRY's functions in anti-tumor progression and invasion/metastasis are mediated through modifying the fundamental histopathological changes of tumor cells (i.e. architecture, polarity, differentiation, motility and adhesion), likely by regulating Hippo-NDR and other downstream pathways. The long-term goals of our research are to elucidate the molecular mechanisms of FRY in inhibiting BCa progression and invasion/metastasis and explore the diagnostic and therapeutic applications of FRY in BCa. To this end, we will define the effects of FRY on tumor progression and invasion/metastasis (Aim 1a) and examine and compare the different effects of the wildtype or functionally mutated form of human FRY gene in modifying tumor cell architecture, adhesion, motility and invasion (Aim 1b). Within the molecular focus of Aim 2, we will examine the relationship between FRY and Hippo-NDR pathway and determine its role in FRY-mediated anti-tumor progression and invasion/metastasis functions. In addition, we propose to explore and identify other FRY-regulated signal pathway(s) and partner proteins (Exploratory Aim). The experiments proposed are envisioned to mechanistically define the effect of FRY on tumor progression and invasion/metastasis.